In a conventional electrophotographic image forming device, an electrostatic latent image is formed on a surface of a photosensitive drum after the surface is charged and then exposed to light. Toner is subsequently supplied to the electrostatic latent image, thereby forming a visible toner image to be transferred onto sheets. For charging the surface of the photosensitive drum, there has been used a charger, such as a charging wire for generating a corona discharge.
When rotating the photosensitive drum for the purpose of warming up or cleaning, a voltage is applied to the charger (charging member) for making the surface of the photosensitive drum charged with a potential higher than that of a developing roller in order to prevent toner adhesion to the photosensitive drum. The voltage applied to the photosensitive drum for a purpose other than development is conventionally the same as a voltage applied for development, which has a relatively high absolute value. As a result, given a fact that the life of the charging member is dependent on the level of voltage applied thereto, continuous applications of such a high voltage to the photosensitive drum may result in encouraging adherence of foreign materials to the charging member, thereby leading to a malfunction of the charging member and a shorter life of the charging member.